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| How Soon Can I Build a Fire? |
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| Concrete and mortar made with Portland cement, cures to about 60% of full strength in 24 hours and nearly all of the water used to mix the mortar has been used up in the "hydrolic", or chemical, reaction. Portland based concrete and mortar, however, dosen't reach full strength until cured for 28 days, so many masons tell you to wait 28 days until you use the fireplace.
While there may be some moisture left in the masonry it is more likely to be excess moisture or moisture from rain or washing and even in 28 days the masonry may still contain moisture. You don't want to heat this moisture up so fast or hot that it boils, which could damage the masonry, but a good way to dry out the chimney is to build a fire in the fireplace.
The refractory materials (firebrick, throat, smoke chamber, & flues) which are the only materials in the fireplace likely to get very hot, have been made and fired in a kiln, don't need to be curred and are fully ready to use.
The refractory mortar used to lay the firebrick and lining components has not been curred but it is a modern refractory product that can be dried or cured and fired within 24 hours.
Modern refractory materials have been developed mostly for industrial furnaces and kilns. They are not going to shut down a steel mill or glass factory for 28 days after repairs to the kiln and in fact the instructions for refractory products recommend curing after 24 hours by bringing the temperature in the kiln or furnace up to operating temperature at a rate of 50 degrees F per hour. The old guys say "we just used to build a wood fire in the kiln to cure it".
So, after 24 hours, build a modest wood fire in your new fireplace to cure it and break it in. |
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